Structure and method for air gap interconnect integration

ABSTRACT

Methods for producing air gap-containing metal-insulator interconnect structures for VLSI and ULSI devices using a photo-patternable low k material as well as the air gap-containing interconnect structure that is formed are disclosed. More particularly, the methods described herein provide interconnect structures built in a photo-patternable low k material in which air gaps are defined by photolithography in the photo-patternable low k material. In the methods of the present invention, no etch step is required to form the air gaps. Since no etch step is required in forming the air gaps within the photo-patternable low k material, the methods disclosed in this invention provide highly reliable interconnect structures.

RELATED APPLICATIONS

This application is related to co-pending and co-assigned U.S.application Ser. No. 12/721,032, entitled “METHODS FOR FABRICATION OF ANAIR GAP-CONTAINING INTERCONNECT STRUCTURE” filed Mar. 10, 2010, andco-pending and co-assigned U.S. application Ser. No. 12/768,267,entitled “STRUCTURES AND METHODS FOR AIR GAP INTEGRATION” filed Apr. 27,2010, the entire contents of which are both incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to air gap-containing metal-insulatorinterconnect structures for Very Large Scale Integrated (VLSI) andUltra-Large Scale Integrated (ULSI) devices and methods of forming thesame.

BACKGROUND OF THE INVENTION

Interconnect structures in integrated circuits induce a delay in thepropagation of the information between semiconductor devices such astransistors. To reduce this delay, the interconnect structures shouldposses the lowest capacitance possible. One approach to forminterconnect structures with the lowest possible capacitance is tointroduce air (or vacuum) gaps into the interconnect dielectric part ofthe interconnect structure; by replacing a portion of the dielectricmaterial with an air gap, the capacitance can be reduced dramatically.

Among several integration schemes proposed for air gap integration, adielectric etch back scheme is the most commonly used. See, for example,Arnal et al. 2001 Proc. IEEE International Interconnect TechnologyConference, pages 398-400. In this scheme, the gap is etched in adielectric cap between two metal lines, and eventually transferred intothe dielectric material. After transferring the gap into the dielectricmaterial, the dielectric material is isotropically removed between thetwo metal lines. A dielectric deposition process is then performed thatpinches off the gap such that the next interconnect level can befabricated.

There are several problems with the aforementioned prior art air gapfabrication scheme. First, the above mentioned prior art air gapfabrication scheme requires a very accurate lithographic step to definetrenches between the metal lines. Furthermore, the above mentioned priorart scheme requires an etch step to remove the dielectric in between themetal lines. If the lithography step is not perfect (misalignment, ortoo large an opening may result) and, if the etch step leads to a widthincrease, the metal lines can be damaged by this etch step. Theisotropic etch process may also damage the sidewalls of the metal lineor the interface between the metal lines and an overlying cap layer.Both issues may lead to reliability issues.

Finally, the need for very high resolution lithography and a criticaletch step leads to a huge increase in the cost of the air gap module.Thus, there is a need for a simplified integration scheme that leads tocheap and reliable air gap-containing interconnect structures.

SUMMARY

The present invention relates to methods for producing airgap-containing metal-insulator interconnect structures for VLSI and ULSIdevices using a photo-patternable low k (PPLK) material as well as theair gap-containing interconnect structure formed thereby. Moreparticularly, the methods described herein provide interconnectstructures built in a photo-patternable low k material in which air gapsare defined by photolithography in the photo-patternable low k material.In the methods of the present invention, no etch step is required toform the air gaps. Since no etch step is required in forming the airgaps within the photo-patternable low k material, the methods disclosedin this invention provide highly reliable interconnect structures.

In one aspect of the present disclosure, an air gap-containinginterconnect structure is provided in which a patterned and cured PPLKmaterial includes a plurality of electrically conductive filled regionsand air gaps that are located between neighboring (vertically and/orhorizontally) electrically conductive filled regions. Specifically, theair gap-containing interconnect structure includes a substrate, amaterial stack located on an upper surface of the substrate, a patternedfirst low k material located on an uppermost surface of the materialstack, a patterned second low k material located on an upper surface ofthe patterned first low k material, a patterned and curedphoto-patternable low k (PPLK) material located on an upper surface ofthe patterned second low k material, and a dielectric cap located on anupper surface of the patterned and cured PPLK material. The patternedand cured PPLK material has a plurality of electrically conductivefilled regions and air gaps located therein. At least a lower portion ofone of the plurality of electrically conductive filled regions extendsthrough the patterned first and second low k materials. Moreover, one ofthe air gaps of the structure disclosed herein includes an extendedwidth lower portion that is present in the first patterned low kmaterial and is connected with the one of the air gaps in the patternedand cured PPLK material by an opening within the patterned second low kmaterial.

In one embodiment of the present invention, the plurality ofelectrically conductive filled regions as well as the air gaps withinthe patterned and cured PPLK material have a sub-lithographic width,i.e., a width of 10 nm to 40 nm.

In another aspect of the invention, a method of forming an airgap-containing interconnect structure is provided. The method includesproviding a patterned mask on a surface of an initial structure, theinitial structure including a substrate, a material stack located on anupper surface of the substrate, a first low k material located on anuppermost surface of the material stack, and a second low k materiallocated on an upper surface of the first low k material, wherein thepatterned mask has at least one first opening that exposes a portion ofthe second low k material. The exposed portion of the second low kmaterial is then etched utilizing the patterned mask as an etch mask toform a patterned second low k material having the one first openingtherein. A patterned photoresist is formed on an upper surface of thepatterned second low k material, wherein a portion of the patternedphotoresist fills the at least one first opening within the patternedsecond low k material. The patterned photoresist has at least one secondopening that exposes a portion of the patterned second low k material.The exposed portion of the patterned second low k material as well asunderlying portion of the first low k material are then etched utilizingthe patterned photoresist as an etch mask to form a patterned second lowk material having the one first opening and an upper portion of the atleast one second opening therein and a patterned first low k materialhaving a lower portion of the at least one second opening therein. Apatterned and cured photo-patternable low k (PPLK) material having aplurality of electrically conductive filled regions and gaps locatedtherein is formed atop the patterned second low k material, wherein atleast one of the plurality of electrically conductive filled regions islocated within the at least one second opening and wherein one of thegaps is located above and connected with the at least one first openinglocated within the patterned second low k material. A lateral etchingprocess is then performed that forms an expanded width gap within thepatterned first low k material which is located beneath and connectedwith the at least one first opening formed in the patterned second low kdielectric material. A dielectric cap is formed atop the patterned andcured PPLK material forming air gaps at least within the PPLK material.

In one embodiment, the patterned mask is a patterned photoresist formedby lithography, while in another embodiment, the patterned mask is aself-assembled co-polymer mask formed utilizing a self-assembling blockcopolymer, annealing the self-assembling block copolymer into aself-assembled block copolymer and removing at least one of thepolymeric components of the self-assembled block copolymer. Theself-assembled co-polymer mask has sub-lithographic features.

BRIEF DESCRIPTION OF SEVRAL VIEWS OF THE DRAWINGS

FIG. 1 is a pictorial representation (through a cross sectional view)depicting an initial structure including, from bottom to top, asubstrate, a material stack, a first low k material, a second low kmaterial and a first patterned photoresist including at least one firstopening therein that can be employed in one embodiment of the presentdisclosure.

FIG. 2 is a pictorial representation (through a cross sectional view)depicting the initial structure of FIG. 1 after transferring the atleast one first opening into the second low k material forming apatterned second low k material having the at least one first openingand removal of the first patterned photoresist.

FIG. 3 is a pictorial representation (through a cross sectional view)depicting the structure of FIG. 2 after forming a second patternedphotoresist including at least one second opening therein atop thepatterned second low k material and within the at least one firstopening in the patterned second low k material.

FIG. 4 is a pictorial representation (through a cross sectional view)depicting the structure of FIG. 3 after transferring the at least onesecond opening into the patterned second low k material and theunderlying first low k material and removal of the second patternedphotoresist.

FIG. 5 is a pictorial representation (through a cross sectional view)depicting the structure of FIG. 4 after forming a patterned and curedphoto-patternable low k material having a plurality of electricallyconductive filled regions and gaps located therein, wherein at least oneof the plurality of electrically conductive filled regions is locatedwithin the at least one second opening and wherein one of the gaps islocated above and connected with the at least one first opening locatedwithin the patterned second low k material.

FIG. 6 is a pictorial representation (through a cross sectional view)depicting the structure of FIG. 5 after performing a lateral etchingprocess that forms an expanded width gap within the patterned first lowk material which is located beneath and connected with the at least onefirst opening formed in the second low k dielectric material.

FIG. 7 is a pictorial representation (through a cross sectional view)depicting the structure of FIG. 6 after forming a dielectric cap atopthe patterned and cured photo-patternable low k material forming airgaps within the structure.

FIG. 8 is a pictorial representation (through a cross sectional view)depicting an initial structure including from bottom to top, asubstrate, a material stack, a first low k material, a second low kmaterial and a self-assembled co-polymer mask including a plurality ofopenings therein that can be employed in another embodiment of thepresent disclosure.

FIG. 9 is a pictorial representation (through a cross sectional view)depicting the initial structure of FIG. 8 after etching exposed portionsof the second low k material and removal of the self-assembledco-polymer mask.

FIG. 10 is a pictorial representation (through a cross sectional view)depicting the structure of FIG. 9 after forming a patterned photoresisthaving at least one opening therein that exposes at least one openingwithin the previously etched second low k material.

FIG. 11 is a pictorial representation (through a cross sectional view)depicting the structure of FIG. 10 after etching exposed portions of thefirst low k material and removal of the patterned photoresist.

FIG. 12 is a pictorial representation (through a cross sectional view)depicting the structure of FIG. 11 after forming a patterned and curedphoto-patternable low k material having a plurality of electricallyconductive filled regions and gaps located therein, wherein at least oneof the plurality of electrically conductive filled regions is locatedwithin an opening that is present in the previously etched portions ofthe first low k material.

FIG. 13 is a pictorial representation (through a cross sectional view)depicting the structure of FIG. 12 after performing a lateral etch thatexpands the width of at least one of the gaps.

FIG. 14 is a pictorial representation (through a cross sectional view)depicting the structure of FIG. 13 after forming a dielectric cap atopthe patterned and cured photo-patternable low k material forming airgaps within the structure.

DETAILED DESCRIPTION

The present invention, which provides air gap-containing interconnectstructures and methods of fabricating such air gap-containinginterconnect structures, will now be described in greater detail byreferring to the following discussion and drawings that accompany thepresent application. It is observed that the drawings of the presentapplication are provided for illustrative purposes and, as such, thedrawings are not drawn to scale.

In the following description, numerous specific details are set forth,such as particular structures, components, materials, dimensions,processing steps and techniques, in order to provide an understanding ofsome aspects of the present invention. However, it will be appreciatedby one of ordinary skill in the art that the invention may be practicedwithout these specific details. In other instances, well-knownstructures or processing steps have not been described in detail inorder to avoid obscuring the invention.

It will be understood that when an element as a layer, region orsubstrate is referred to as being “on” or “over” another element, it canbe directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “beneath” or “under” another element, it can bedirectly beneath or under the other element, or intervening elements maybe present. In contrast, when an element is referred to as being“directly beneath” or “directly under” another element, there are nointervening elements present.

As stated above, methods for producing a metal-insulator interconnectstructure having air gaps for VLSI and ULSI devices using aphoto-patternable low k (PPLK) material are disclosed. Moreparticularly, the methods disclosed herein provide interconnectstructures including a photo-patternable low k material in which airgaps are defined by photolithography in the photo-patternable low kmaterial. With such methods, no etch step is needed to form the airgaps.

It is noted that the photo-patternable low k materials employed in theinvention are any dielectric materials possessing the following twofunctions. They act as a photoresist during a patterning process and aresubsequently converted into a low k dielectric insulator during a postpatterning cure process. The cured product of a photo-patternable low kmaterial, therefore, can serve as a permanent on-chip dielectricinsulator. The photo-patternable low k material can be deposited from aliquid phase. In the present invention, the terms “cure” or “curing” areused interchangeably to refer to one of the processes selected from athermal cure, an electron beam cure, an ultra-violet (UV) cure, an ionbeam cure, a plasma cure, a microwave cure or a combination thereof. A“cured” product of a photo-patternable low k material is the product ofthe photo-patternable low k material after it has undergone one of theaforementioned cure processes. The “cured” product of aphoto-patternable low k material is different from the photo-patternablelow k material in chemical nature and physical, mechanical andelectrical properties.

The term “photo-patternable low k material (or PPLK for short)” includesa functionalized polymer, copolymer or blend including at least two ofany combination of polymers and/or copolymers having one or moreacid-sensitive imageable groups. The PPLK material acts as a photoresistand after curing it is converted from a photoresist into a permanenton-chip dielectric material having a dielectric constant of about 4.3 orless. It is noted that when the PPLK material is comprised of a polymer,the polymer includes at least one monomer (to be described in greaterdetail below). When the PPLK material is comprised of a copolymer, thecopolymer includes at least two monomers (to be described in greaterdetail below). The blends of polymers and/or copolymers include at leasttwo of any combination of polymers and/or copolymers described below.

In general terms, the PPLK material that can be employed is aphoto-patternable composition including a polymer, a copolymer, or ablend including at least two of any combination of polymers and/orcopolymers, wherein the polymers include one monomer and the copolymersinclude at least two monomers and wherein the monomers of the polymersand the monomers of the copolymers are selected from a siloxane, silane,carbosilane, oxycarbosilane, silsesquioxane, alkyltrialkoxysilane,tetra-alkoxysilane, unsaturated alkyl substituted silsesquioxane,unsaturated alkyl substituted siloxane, unsaturated alkyl substitutedsilane, an unsaturated alkyl substituted carbosilane, unsaturated alkylsubstituted oxycarbosilane, carbosilane substituted silsesquioxane,carbosilane substituted siloxane, carbosilane substituted silane,carbosilane substituted carbosilane, carbosilane substitutedoxycarbosilane, oxycarbosilane substituted silsesquioxane,oxycarbosilane substituted siloxane, oxycarbosilane substituted silane,oxycarbosilane substituted carbosilane, and oxycarbosilane substitutedoxycarbosilane.

More specifically, the PPLK material that can be employed is aphoto-patternable composition comprising a photo/acid-sensitive polymerof one monomer or a copolymer of at least two monomers selected fromsiloxane, silane, carbosilane, oxycarbosilane, organosilicates,silsesquioxanes and the like. The PPLK material may also be aphoto-patternable composition comprising a polymer of one monomer or acopolymer of at least two monomers selected from alkyltrialkoxysilane,tetra-alkoxysilane, unsaturated alkyl (such as vinyl) substitutedsilsesquioxane, unsaturated alkyl substituted siloxane, unsaturatedalkyl substituted silane, an unsaturated alkyl substituted carbosilane,unsaturated alkyl substituted oxycarbosilane, carbosilane substitutedsilsesquioxane, carbosilane substituted siloxane, carbosilanesubstituted silane, carbosilane substituted carbosilane, carbosilanesubstituted oxycarbosilane, oxycarbosilane substituted silsesquioxane,oxycarbosilane substituted siloxane, oxycarbosilane substituted silane,oxycarbosilane substituted carbosilane, and oxycarbosilane substitutedoxycarbosilane. Additionally, the PPLK material may comprise a blendincluding at least two of any combination of polymers and/or copolymers,wherein the polymers include one monomer and the copolymers include atleast two monomers and wherein the monomers of the polymers and themonomers of the copolymers are selected from a siloxane, silane,carbosilane, oxycarbosilane, silsesquioxane, alkyltrialkoxysilane,tetra-alkoxysilane, unsaturated alkyl substituted silsesquioxane,unsaturated alkyl substituted siloxane, unsaturated alkyl substitutedsilane, an unsaturated alkyl substituted carbosilane, unsaturated alkylsubstituted oxycarbosilane, carbosilane substituted silsesquioxane,carbosilane substituted siloxane, carbosilane substituted silane,carbosilane substituted carbosilane, carbosilane substitutedoxycarbosilane, oxycarbosilane substituted silsesquioxane,oxycarbosilane substituted siloxane, oxycarbosilane substituted silane,oxycarbosilane substituted carbosilane, and oxycarbosilane substitutedoxycarbosilane.

Optionally the PPLK material may be photo-patternable compositionfurther comprising at least one microscopic pore generator (porogen).The pore generator may be or may not be photo/acid sensitive.

Illustrative polymers for the PPLK material include, but are not limitedto siloxane, silane, carbosilane, oxycarbosilane, silsesquioxane-typepolymers including caged, linear, branched or combinations thereof. Inone embodiment, the PPLK material is a photo-patternable compositioncomprising a blend of these photo/acid-sensitive polymers. Examples ofPPLK materials that can be employed in this application are disclosed,for example, in U.S. Pat. Nos. 7,041,748, 7,056,840, and 6,087,064, aswell as U.S. Patent Application Publication No. 2008/0286467, U.S.Patent Application Publication No. 2009/0233226, U.S. Patent ApplicationPublication No. 2009/0291389, U.S. patent application Ser. No.12/569,200, filed Sep. 29, 2009 all of which are incorporated herein byreference in their entirety.

The PPLK material is typically formed from a positive-tonephoto-patternable composition that includes at least one of the abovementioned polymers, copolymers or blends, a photoacid generator, a baseadditive and a solvent typically used in a photoresist composition. By“positive-tone” it is meant that the part of the PPLK material that isexposed to photolithography will be removed by a conventional developer,while the unexposed part of the PPLK material is not removed. Thephotoacid generators, base additives and solvents are well known tothose skilled in the art and, as such, details regarding thosecomponents are not fully provided.

One method of the present invention which includes the use of the PPLKmaterial described above will now described in greater detail. Referenceis first made to FIGS. 1-7 which illustrate an embodiment of the presentapplication. In this illustrated embodiment, a positive-tone PPLKmaterial, as described above, is deposited atop an initial structureincluding, from bottom to top, a substrate, a material stack, apatterned first low k material and a patterned second low k material.The material stack can include a dielectric cap, an antireflectivecoating (ARC) or a multilayered stack thereof. Standard interconnectstructures are built into the positive-tone PPLK material using standardsingle or dual damascene methods well known to those skilled in the art.The positive-tone PPLK material maintains its photosensitive propertyduring the interconnect build up. A photolithography step is employedafter the interconnect structure build up to define the position of airgaps in-between at least one pair of neighboring electrically conductivefilled openings. Since the electrically conductive filled openings arenot sensitive to ultra violet radiation, the lithography requirements interms of the dimension and alignment are relaxed. The positive-tone PPLKmaterial exposed in the lithography step is removed by a conventionaldeveloper leaving gaps in-between at least one pair of electricallyconductive filled openings. After forming the gaps, the remaining PPLKmaterial is cured forming a patterned and cured permanent low kdielectric including gaps in-between at least one pair of electricallyconductive filled openings. A dielectric cap is then formed atop thepatterned and cured low k dielectric material sealing off the gapsforming an air gap-containing interconnect structure in which the airgaps are formed within at least the patterned and cured permanent low kdielectric material in-between the at least one pair of electricallyconductive filled openings. The air gaps also extend into the patternedsecond low k material and the patterned first low k material. Within thepatterned first low k material, each air gap has an expanded widthrelative to the width of the corresponding air gap in at least thepatterned and cured PPLK material.

Reference is now made to FIG. 1 which illustrates an initialinterconnect structure 10 that can be employed in one embodiment of theinvention. The initial interconnect structure 10 of FIG. 1 includes asubstrate 12, a material stack 16, a first low k material 18, a secondlow k material 20 and a first patterned photoresist 22, i.e., patternedmask, having at least one first opening 24 located therein.

The substrate 12 may comprise a semiconducting material, an electricallyinsulating material, an electrically conductive material, devices orstructures made of these materials or any combination thereof (e.g., alower level of an interconnect structure). When the substrate 12 iscomprised of a semiconducting material, any semiconductor such as Si,SiGe, SiGeC, SiC, Ge alloys, GaAs, InAs, InP and other III/V or II/VIcompound semiconductors, or organic semiconductors may be used. Thesubstrate 12 may also be a flexible substrate containing devices thatare suitable for high-speed roll-to-roll processing. In addition tothese listed types of semiconducting materials, substrate 12 may also bea layered semiconductor such as, for example, Si/SiGe, Si/SiC,silicon-on-insulators (SOIs) or silicon germanium-on-insulators (SGOIs).These semiconductor materials may form a device, or devices orstructures, which may be discrete or interconnected. These devices anddevice structures may be for computation, transmission, storage ordisplay of information, such as logic devices, memory devices, switchesor display devices. In some embodiments, one or more semiconductordevices such as, for example, complementary metal oxide semiconductor(CMOS) devices, strained silicon devices, carbon-based (e.g., carbonnanotubes and/or graphene) devices, phase-change memory devices,magnetic memory devices, magnetic spin switching devices, singleelectron transistors, quantum devices, molecule-based switches and otherswitching or memory devices that can be part of an integrated circuit,can be fabricated on the semiconducting material.

When the substrate 12 is an electrically insulating material, theinsulating material can be an organic insulator, an inorganic insulatoror a combination thereof including multilayers. The electricallyinsulating materials may be part of a device, or devices or structures,which may be discrete or interconnected. These devices and structuresmay be for logic applications or memory applications.

When the substrate 12 is an electrically conducting material, thesubstrate may include, for example, polySi, an elemental metal, an alloyincluding at least one elemental metal, a metal silicide, a metalnitride, carbon nanotubes, graphene or combinations thereof includingmultilayers.

In yet other embodiments, substrate 12 can be composed of one of theantireflective coating materials described herein below.

Atop the substrate 12 is a material stack 16 that may include adielectric cap, an antireflective coating, or a multilayered stackthereof. When present, the dielectric cap of material stack 16 is formeddirectly on the surface of substrate 12 utilizing a standard depositionprocess such as, for example, chemical vapor deposition (CVD), plasmaenhanced chemical vapor deposition (PECVD), atomic layer deposition(ALD), chemical solution deposition, or evaporation. The dielectric capcomprises any suitable dielectric capping material such as, for example,SiC, SiN, SiO₂, a carbon doped oxide, a nitrogen and hydrogen dopedsilicon carbide SiC(N,H) or multilayers thereof. The dielectric cap canbe a continuous layer or a discontinuous layer. The dielectric cap canbe a layer with graded composition in the vertical direction. It canalso be a select cap, such as CoWP.

A post deposition treatment may be applied to the dielectric cap tomodify the properties of either the entire layer or the surface of thedielectric cap. This post deposition treatment can be selected from heattreatment, irradiation of electromagnetic wave (such of ultra-violetlight), particle beam (such as an electron beam, or an ion beam), plasmatreatment, chemical treatment through a gas phase or a liquid phase(such as application of a monolayer of surface modifier) or anycombination thereof. This post-deposition treatment can be blanket orpattern-wise. The purpose of the post deposition treatment is to enhancethe chemical, physical, electrical, and/or mechanical properties of thedielectric cap, such as adhesion strength. The chemical propertiesinclude the nature and/or location of surface functional groups, andhydrophilicity. The physical properties include density, moistureabsorption, and heat conductivity. The mechanical properties includemodulus, hardness, cohesive strength, toughness, resistance to crack andadhesion strength to its neighboring layers. The electrical propertiesinclude dielectric constant, electrical breakdown field, and leakagecurrent.

The heat treatment should be no higher than the temperature that theunderlying substrate can withstand, usually 500° C. This heat treatmentcan be conducted in an inert environment or within a chemicalenvironment in a gas phase or a liquid phase. This treatment step may ormay not be performed in the same tool as that used in forming theoptional dielectric cap.

The post deposition treatment by irradiation of electromagnetic wave canbe by ultra-violet (UV) light, microwave and the like. The UV light canbe broadband with a wavelength range from 100 nm to 1000 nm. It can alsobe UV light generated by an excimer laser or other UV light source. TheUV treatment dose can be a few mJ/cm² to thousands of J/cm². Thisirradiation treatment can be conducted at ambient temperature or at anelevated temperature no higher than 500° C. This irradiation treatmentcan be conducted in an inert environment or within a chemicalenvironment in a gas phase or a liquid phase. The following conditionscan be employed for this aspect of the present disclosure: a radiationtime from 10 sec to 30 min, a temperature from room temperature to 500°C., and an environment including vacuum, or gases such as, for example,inert gas, N₂, H₂, O₂, NH₃, hydrocarbon, and SiH₄. This treatment stepmay or may not be performed in the same tool as that used in forming thedielectric cap.

The post deposition treatment by plasma treatment can be selected froman oxidizing plasma, a reducing plasma or a neutral plasma. Oxidizingplasmas include, for example, O₂, CO, and CO₂. Reducing plasmas include,for example, H₂, N₂, NH₃, and SiH₄. The neutral plasmas include, forexample, Ar and He. A plasma treatment time from 1 sec to 10 min and aplasma treatment temperature from room temperature to 400° C. can beemployed. This treatment step may or may not be performed in the sametool as that used in forming the dielectric cap.

The post deposition chemical treatment may be conducted in a gas phaseor a liquid phase. The following conditions may be employed for thisaspect of the present invention: a treatment time from 1 sec to 30 min,a temperature from room temperature (i.e., from 20° C. to 30° C.) to500° C. Chemicals suitable for this chemical treatment may be selectedfrom any chemicals that improve chemical, physical, electrical, and/ormechanical properties of the dielectric cap layer, such as adhesionstrength. This chemical treatment may penetrate the entire optionaldielectric cap or is limited only to the surface of the optionaldielectric cap. Example chemicals include adhesion promoters such assilanes, siloxanes and silylation agents. This treatment step may or maynot be performed in the same tool as that used in forming the dielectriccap.

The thickness of the dielectric cap may vary depending on the techniqueused to form the same as well as the material make-up of the layer.Typically, the dielectric cap has a thickness from 1 nm to 100 nm, witha thickness from 20 nm to 45 nm being more typical.

The antireflective coating (ARC) of material stack 16 can be formed on asurface of the dielectric cap if present, or directly on a surface ofthe substrate 12 when the dielectric cap is not present. Although, theARC is optional, it is typically present when at least one of theoverlying layers (e.g., the first low k material, the second low kmaterial or the PPLK material) serves as a photoresist material. The ARCemployed has all of the following general characteristics: (i) It actsas an ARC during a lithographic patterning process; (ii) It withstandshigh-temperature BEOL integration processing (up to 500° C.); (iii) Itprevents poisoning of at least one of the overlying layers that serve asa photoresist (e.g., the first low k material, the second low k materialand/or the PPLK material) by the substrate; (iv) It provides verticalwall profile and sufficient etch selectivity between one of theoverlying layers (e.g., the first low k material, the second low kmaterial and the PPLK material) and the ARC layer; (v) It serves as apermanent dielectric layer in a chip (low dielectric constant,preferably k<5, more preferably k<3.6); and (vi) It is compatible withconventional BEOL integration and produces reliable hardware.

Further discussion is now provided for characteristics (i)-(v).

Characteristic (i) the ARC acts as an antireflective coating (ARC)during a lithographic patterning process: ARC may be designed to controlreflection of light that is transmitted through a photoresist materialsuch as one of the low k materials or the PPLK material employed in thepresent invention, reflected off the substrate 12 and back into thephotoresist material, where it can interfere with incoming light andcause the photoresist material to be unevenly exposed. The ARC's opticalconstants are defined here as the index of refraction n and theextinction coefficient k. In general, ARC can be modeled so as to findoptimum optical parameters (n and k values) of the ARC as well asoptimum thickness. The preferred optical constants of ARC are in therange from n=1.2 to n=3.0 and k=0.01 to k=0.9, preferably n=1.4 to n=2.6and k=0.02 to k=0.78 at a wavelength of 365, 248, 193 and 157, 126 nmand extreme ultraviolet (13.4 nm) radiation. The optical properties andthickness of the ARC are optimized to obtain optimal resolution, profilecontrol and to maximize the process window of the photoresist materialduring the subsequent patterning steps, which is well known to thoseordinarily skilled in the art.

Characteristic (ii) the ARC can withstand high-temperature BEOLintegration processing (up to 500° C.): The ARC must withstand the harshprocessing conditions during BEOL integration. These include hightemperature and intense UV cure. The process temperature can be as highas 450° C. The intensity of the light used in the UV cure process can beas high as tens of J/cm².

Characteristic (iii) the ARC prevents photoresist material poisoning bythe substrate: At least the PPLK material and optionally the low kmaterials employed herein include a chemically amplified resist. Theycan be poisoned by any basic containment from the underlying substrate,such as a SiCN cap layer. The ARC must serve as a barrier layer toprevent basic contaminant from the underlying substrate from diffusinginto the photoresist material to poison the same.

Characteristic (iv) the ARC provides vertical wall profile andsufficient etch selectivity between the photoresist material and the ARClayer: the ARC should provide sufficient reflectivity control withreflectivity from the underlying substrate under a particularlithographic wavelength of less than 8%, preferably less than 5%, morepreferably less than 2% and generate vertical side wafer profile. TheARC should also generate residue-free patterns with no footing.Moreover, the adhesion of the photoresist material should be sufficientto prevent pattern collapse. The ARC should also be designed such thatthe etch selectivity during a subsequent ARC/cap open process issufficiently high so that the opening of the ARC/cap stack does noterode a significant portion of the photoresist material and degradesignificantly its pattern profile. An etch selectivity (etch rate ratioof ARC/cap versus photoresist material) is greater than 1, preferablygreater than 3, more preferable greater than 5.

Characteristic (v) the ARC serves as a permanent dielectric layer in achip: The ARC remains after forming the air gaps and thus serves as apermanent dielectric layer in a chip. Therefore, ARC must meet therequirements of an on-chip dielectric insulator, including electricalproperties (low dielectric constant: preferably k less than 5, and morepreferably k less than 3.6; dielectric breakdown field: greater than 2MV/cm, preferably greater than 4 MV/cm, and more preferably greater than6 MV/cm, leakage: less than 10⁻⁹ A/cm², preferably less than 10⁻⁷ A/cm²,and more preferably less than 10⁻⁹ A/cm²); mechanical properties(adhesion energy is equal to or greater than the cohesive energy of theweakest layer of the integrated film stack); and the ARC employed mustpass electrical and mechanical reliability tests.

The thickness of the ARC may vary depending on the technique used toform the same as well as the material make-up of the layer. Typically,the ARC has a thickness from 1 nm to 200 nm, with a thickness from 10 nmto 140 nm being more typical. The ARC may be inorganic or a hybrid ofinorganic and organic. The ARC may be a single layer or multilayer. Itmay also be a graded ARC with graded composition in the verticaldirection.

Inorganic antireflective coatings, such as silicon oxynitride (SiON),silicon carbide (SiC), silicon oxycarbide (SiOC), SiCOH, siloxane,silane, carbosilane, oxycarbosilane, and silsesquioxane, either as apolymer or a copolymer may be employed as the ARC and may be deposited,for example, by plasma-enhanced chemical vapor deposition, spin-ontechniques, spray coating, dip coating, etc. The ARC may be a singlelayer or multilayer. When the ARC is a multilayer ARC, the deposition ofeach layer may be the same or a combination of deposition methods can beused. The chemical composition of the ARC may be uniform or graded alongthe vertical direction. After applying the ARC particularly those from aliquid phase, a post deposition baking step is usually required toremove unwanted components, such as solvent, and to effect crosslinking.The post deposition baking step of the ARC is typically, but notnecessarily always, performed at a temperature from 80° C. to 300° C.,with a baking temperature from 120° C. to 200° C. being more typical.

In some embodiments, the as-deposited ARC may be subjected to a postdeposition treatment to improve the properties of the entire layer orthe surface of the ARC. This post deposition treatment can be selectedfrom heat treatment, irradiation of electromagnetic wave (such asultra-violet light), particle beam (such as an electron beam, or an ionbeam), plasma treatment, chemical treatment through a gas phase or aliquid phase (such as application of a monolayer of surface modifier) orany combination thereof. This post-deposition treatment can be blanketor pattern-wise. The purpose of this post deposition treatment is toenhance the chemical, physical, electrical, and/or mechanical propertiesof the ARC and/or the film stack, such as adhesion strength. Thechemical properties include nature and/or location of surface functionalgroups, and hydrophilicity. The physical properties include density,moisture absorption, and heat conductivity. The mechanical propertiesinclude modulus, hardness, cohesive strength, toughness, resistance tocrack and adhesion strength to its neighboring layers. The electricalproperties include dielectric constant, electrical breakdown field, andleakage current.

The conditions described above for the post treatment of the dielectriccap may be used for the post treatment for the ARC.

In one embodiment, the ARC that is employed is an inorganic compositionthat includes elements of M, C (carbon) and H (hydrogen), wherein M isselected from at least one of the elements of Si, Ge, B, Sn, Fe, Ta, Ti,Ni, Hf and La. Such an ARC is described for example in U.S. PatentPublication No. 2009/0079076 the entire content of which is incorporatedherein by reference. This inorganic ARC may optionally include elementsof O, N, S, F or mixtures thereof. In some embodiments, M is preferablySi. In some embodiments, the ARC composition may also be referred to asa vapor deposited M:C:H: optionally X material, wherein M is as definedabove, C and H are carbon and hydrogen element, respectively, and X isat least one element of O, N, S and F.

In one embodiment, the ARC is produced by a vapor or liquid phasedeposition (such as, for example, CVD, PECVD, PVD, ALD and spin-oncoating) method using appropriate precursors or combination ofprecursors containing elements described above.

In a preferred embodiment, the ARC is a Si:C:H:X film. These Sicontaining films are deposited from at least one Si containingprecursor. More particularly, the Si:C:H:X films are deposited from atleast one Si containing precursor with, or without, additions ofnitrogen and/or oxygen and/or fluorine and/or sulfur containingprecursors. The Si containing precursor that is employed can compriseany Si containing compound including molecules selected from silane(SiH₄) derivatives having the molecular formula SiR₄, cyclic Sicontaining compounds including cyclocarbosilane where the Rsubstitutents may or may not be identical and are selected from H,alkyl, phenyl, vinyl, allyl, alkenyl or alkynyl groups that may belinear, branched, cyclic, polycyclic and may be functionalized withnitrogen containing substituents, any cyclic Si containing compoundsincluding cyclosilanes, and cyclocarbosilanes.

Preferred Si precursors include, but are not limited to silane,methylsilane, dimethylsilane, trimethylsilane, tetramethylsilane,ethylsilane, diethylsilane, triethylsilane, tetraethylsilane,ethylmethylsilane, triethylmethylsilane, ethyldimethylsilane,ethyltrimethylsilane, diethyldimethylsilane,1,1,3,3,-tetrahydrido-1,3-disilacyclobutane; 1,3-disilacyclobutane;1,3-dimethyl-1,3-dihydrido-1,3-disilylcyclobutane; 1,1,3,3,tetramethyl-1,3-disilacyclobutane;1,1,3,3,5,5-hexahydrido-1,3,5-trisilane;1,1,3,3,5,5-hexamethyl-1,3,5-trisilane;1,1,1,4,4,4,-hexahydrido-1,4-disilabutane; and 1,4-bis-trihydrosilylbenzene. Also the corresponding meta substituted isomers, such asdimethyl-1-propyl-3-silabutane; 2-silapropane, 1,3-disilacyclobutane,1,3-disilapropane, 1,5-disilapentane, or 1,4-bis-trihydrosilyl benzenecan be employed.

A single precursor such as silane amine, Si(Net)₄, can be used as thesilicon, carbon and nitrogen source. Another preferred method is amixture of precursors, a Si containing source such as silane, disilane,or a alkylsilane such as tetramethylsilane, or trimethylsilane, and anitrogen containing source such as ammonia, amines, nitriles, aminos,azidos, azos, hydrizos. An additional carbon source and/or carbon andnitrogen containing source comprised of a linear, branched, cyclic orpolycyclic hydrocarbon backbone of —[CH₂]_(n)—, where n is greater thanor equal to 1, and may be substituted by functional groups selected fromalkenes (—C═C—), alkynes amines (—C≡N—), nitriles (—C≡N), amino (—NH₂),azido (—N═N═N—) and azo (—N═N—) may also be required. The hydrocarbonbackbone may be linear, branched, or cyclic and may include a mixture oflinear branched and cyclic hydrocarbon moieties. These organic groupsare well known and have standard definitions that are also well known inthe art. These organic groups can be present in any organic compound.

In some embodiments, the method may further include the step ofproviding a parallel plate reactor, which has an area of a substratechuck from 85 cm² to 750 cm², and a gap between the substrate and a topelectrode from 1 cm to 12 cm. A high frequency RF power is applied toone of the electrodes at a frequency from 0.45 MHz to 200 MHz.Optionally, an additional RF power of lower frequency than the first RFpower can be applied to one of the electrodes. A single source precursoror a mixture of precursors which provide a silicon, carbon and nitrogensource are introduced into a reactor.

The conditions used for the deposition step may vary depending on thedesired final properties of the ARC. Broadly, the conditions used forproviding the ARC comprising elements of Si:C:H:X, include: setting thesubstrate temperature within a range from 100° C. to 700° C.; settingthe high frequency RF power density within a range from 0.1 W/cm² to 2.0W/cm²; setting the gas flow rates within a range from 5 sccm to 10000sccm; setting the inert carrier gases, such as helium (or/and argon)flow rate within a range from 10 sccm to 10000 sccm; setting the reactorpressure within a range from 1 Torr to 10 Torr; and setting the highfrequency RF power within a range from 10 W to 1000 W. Optionally, alower frequency power may be added to the plasma within a range from 10W to 600 W. When the conductive area of the substrate chuck is changedby a factor of X, the RF power applied to the substrate chuck is alsochanged by a factor of X. Gas flows of silane, carbon and/or nitrogengas precursors are flowed into the reactor at a flow rate within a rangefrom 10 sccm to 1000 sccm. While gas precursors are used in the aboveexample, liquid precursors may also be used for the deposition.

The atomic % ranges for M in such ARC materials are as follows:preferably 0.1 atomic % to 95 atomic %, more preferably 0.5 atomic % to95 atomic %, most preferably 1 atomic % to 60 atomic % and most highlypreferably 5 atomic % to 50 atomic %. The atomic % ranges for C in theARC are as follows: preferably 0.1 atomic % to 95 atomic %, morepreferably 0.5 atomic % to 95 atomic %, most preferably 1 atomic % to 60atomic % and most highly preferably 5 atomic % to 50 atomic %. Theatomic % ranges for H in the ARC are as follows: preferably 0.1 atomic %to 50 atomic %, more preferably 0.5 atomic % to 50 atomic %, mostpreferably 1 atomic % to 40 atomic % and most highly preferably 5 atomic% to 30 atomic %. The atomic % ranges for X in the ARC are as follows:preferably O atomic % to 70 atomic %, more preferably 0.5 atomic % to 70atomic %, most preferably 1 atomic % to 40 atomic % and most highlypreferably 5 atomic % to 30 atomic %.

The ARC including elements of M, C and H may have a tunable index ofrefraction and extinction coefficient which can be optionally gradedalong the film thickness to match the optical properties of thesubstrate and the photoresist to be formed directly on it. Thus, theoptical properties and the lithographic features of the ARC are superiorto those obtained by conventional single layer ARC. The ARC's opticalconstants are defined here as the index of refraction n and theextinction coefficient k.

The ARC including elements of M, C and H can be deposited also in aparallel plate PECVD reactor with the substrate positioned on thegrounded electrode. In some embodiments, the ARC can be deposited at asubstrate temperature up to 400° C., and in a high-density plasma typereactor under suitable chosen conditions. It should be noted that bychanging process parameters such as bias voltage, gas mixture, gas flow,pressure and deposition temperature, the film's optical constants can bechanged. In addition, the composition of the starting precursor as wellas the introduction of oxygen, nitrogen, fluorine, and sulfur containingprecursors also allows the tunability of these films.

In another embodiment, the ARC that is employed is formed by a liquiddeposition process including for example, spin-on coating, spraycoating, dip coating, brush coating, evaporation or chemical solutiondeposition. This ARC formed by liquid deposition comprises a polymerthat has at least one monomer unit comprising the formula M-R^(A)wherein M is at least one of the elements of Si, Ge, B, Sn, Fe, Ta, Ti,Ni, Hf and La and R^(A) is a chromophore. Such an ARC is described inU.S. Patent Publication No. 2009/0081418 the entire content of which isincorporated herein by reference. In some embodiments, M within themonomer unit may also be bonded to organic ligands including elements ofC and H, a cross-linking component, another chromophore or mixturesthereof. The organic ligands may further include one of the elements ofO, N, S and F. When the organic ligand is bonded to M, it is bonded toM′ through C, O, N, S, or F.

In other embodiments, the ARC formed by liquid deposition may alsoinclude at least one second monomer unit, in addition to the at leastone monomer unit represented by the formula M-R^(A). When present, theat least one second monomer unit has the formula M′-R^(B), wherein M′ isat least one of the elements of Si, Ge, B, Sn, Fe, Ta, Ti, Ni, Hf andLa, and R^(B) is a cross-linking agent. M and M′ may be the same ordifferent elements. In these two formulae, M and M′ within the monomerunit may be also be bonded to organic ligands including atoms of C andH, a cross-linking component, a chromophore or mixtures thereof. Theorganic ligands may further include one of the elements of O, N, S andF. When the organic ligand is bonded to M and M′, it is bonded to M orM′ through C, O, N, S, or F.

The liquid ARC composition comprising M-R^(A) or M-R^(A) and M′-R^(B)may also comprise at least one additional component, including aseparate crosslinker, an acid generator or a solvent. When liquiddeposition is employed, the ARC is formed by liquid phase deposition ofa liquid composition that includes an inorganic precursor that includeselement of M, C and H, wherein M is at least one of the elements of Si,Ge, B, Sn, Fe, Ta, Ti, Ni, Hf and La. The inorganic precursor used informing the ARC may optionally include elements of O, N, S, F ormixtures thereof. In some embodiments, M is preferably Si. The liquidcomposition also includes, in addition to the inorganic precursor, achromophore, a cross-linking component, an acid generator and solvent.

One embodiment of the inorganic ARC composition used in the liquiddeposition embodiment comprises M-R^(A) and M′-R^(B) units, wherein Mand M′ are at least one of the elements of Si, Ge, B, Sn, Fe, Ta, Ti,Ni, Hf and La or are selected from Group IIIB to Group VIB, Group IIIA,and Group IVA. The inorganic precursor used in forming the ARC mayoptionally include elements of O, N, S, F or mixtures thereof. Oneembodiment of the ARC composition comprises the MO_(y) unit which can beany one of many different metal-oxide forms. An exemplary list of suchmetal-oxide forms for a particular metal is as follows: MO₃; wherein Mis Sc, Y, lanthanide, and Group IIIA; B, Al, Ga or In; MO₄; wherein M isGroup IVB; Ti, Zr or Hf, and Group IVA; Sn or Ge; MO₅; wherein M isGroup VB; V, Nb or Ta; or P. The Group VB metals are also known to formstable metal oxo forms, LMO₃, wherein L is an oxo; LMO; many of thelisted metals form stable acetoacetato-metal complexes; LMO; many of thelisted metals form stable cyclopentadienyl-metal complexes; LMO; whereinL is an alkoxy ligand; M is Sc, Y, or lanthanide, Group IVB, and GroupVB; or LMO; wherein L is an alkyl or phenyl ligand; M is Group IIIA orGroup IVA.

The chromophore, cross-linking component and acid generator that can beused in the liquid deposited ARC are defined in greater detail withrespect to the following preferred embodiment of the present invention.In a preferred embodiment, the ARC formed by liquid deposition ischaracterized by the presence of a silicon-containing polymer havingunits selected from a siloxane, silane, carbosilane, oxycarbosilane,silsesquioxane, alkyltrialkoxysilane, tetra-alkoxysilane, orsilicon-containing and pendant chromophore moieties. The polymercontaining these units may be a polymer containing these units in thepolymer backbone and/or in pendant groups. Preferably, the polymercontains the preferred units in its backbone. The polymer is preferablya polymer, a copolymer, a blend including at least two of anycombination of polymers and/or copolymers, wherein the polymers includeone monomer and the copolymers include at least two monomers and whereinthe monomers of the polymers and the monomers of the copolymers areselected from a siloxane, silane, carbosilane, oxycarbosilane,silsesquioxane, alkyltrialkoxysilane, tetra-alkoxysilane, unsaturatedalkyl substituted silsesquioxane, unsaturated alkyl substitutedsiloxane, unsaturated alkyl substituted silane, an unsaturated alkylsubstituted carbosilane, unsaturated alkyl substituted oxycarbosilane,carbosilane substituted silsesquioxane, carbosilane substitutedsiloxane, carbosilane substituted silane, carbosilane substitutedcarbosilane, carbosilane substituted oxycarbosilane, oxycarbosilanesubstituted silsesquioxane, oxycarbosilane substituted siloxane,oxycarbosilane substituted silane, oxycarbosilane substitutedcarbosilane, and oxycarbosilane substituted oxycarbosilane.

The polymer should be soluble to form a solution and have film-formingcharacteristics conducive to forming an ARC by conventionalspin-coating. In addition to the chromophore moieties discussed below,the silicon-containing polymer also preferably contains a plurality ofreactive sites distributed along the polymer for reaction with thecross-linking component.

Examples of suitable polymers include polymers having the silsesquioxane(ladder, caged, or network) structure. Such polymers preferably containmonomers having structures (I) and (II) below:

where R^(C) comprises a chromophore and R^(D) comprises a reactive sitefor reaction with the cross-linking component.

Alternatively, general linear organosiloxane polymers containingmonomers (I) and (II) can also be used. In some cases, the polymercontains various combinations of monomers (I) and (II) including linearstructures such that the average structure for R^(C)-containing monomersmay be represented as structure (III) below and the average structurefor R^(D)-containing monomers may be represented by structure (IV)below:

where x is from 1 to 1.5. In theory, x may be greater than 1.5, however,such compositions generally do not possess characteristics suitable forspin-coating processes (e.g., they form undesirable gel or precipitatephases).

Generally, silsesquioxane polymers are preferred. If the ordinaryorganosiloxane polymers are used (e.g., monomers of linear structures(I) and (III)), then preferably, the degree of cross-linking isincreased compared to formulations based on silsesquioxanes.

The chromophore-containing groups R^(C) (or R^(A) in the genericdescription above) may contain any suitable chromophore which (i) can begrafted onto the silicon-containing polymer (or M moiety of the genericmonomer defined above) (ii) has suitable radiation absorptioncharacteristics at the imaging wavelength, and (iii) does not adverselyaffect the performance of the layer or any overlying layers.

Preferred chromophore moieties include benzene and its derivatives,chrysenes, pyrenes, fluoranthrenes, anthrones, benzophenones,thioxanthones, and anthracenes. Anthracene derivatives, such as thosedescribed in U.S. Pat. No. 4,371,605 may also be used; the disclosure ofthis patent is incorporated herein by reference. In one embodiment,phenol, hydroxystyrene, and 9-anthracene methanol are preferredchromophores. The chromophore moiety preferably does not containnitrogen, except for possibly deactivated amino nitrogen such as inphenol thiazine.

The chromophore moieties may be chemically attached by acid-catalyzedO-alkylation or C-alkylation such as by Friedel-Crafts alkylation. Thechromophore moieties may also be chemically attached by hydrosilylationof SiH bond on the parent polymer. Alternatively, the chromophore moietymay be attached by an esterification mechanism. A preferred acid forFriedel-Crafts catalysis is HCl.

Preferably, 15 to 40% of the functional groups contain chromophoremoieties. In some instances, it may be possible to bond the chromophoreto the monomer before formation of the silicon-containing polymer. Thesite for attachment of the chromophore is preferably an aromatic groupsuch as a hydroxybenzyl or hydroxymethylbenzyl group. Alternatively, thechromophore may be attached by reaction with other moieties such ascyclohexanol or other alcohols. The reaction to attach the chromophoreis preferably an esterification of the alcoholic OH group.

R^(D) (or R^(B) in the generic description above) comprises a reactivesite for reaction with a cross-linking component. Preferred reactivemoieties contained in R^(D) are alcohols, more preferably aromaticalcohols (e.g., hydroxybenzyl, phenol, hydroxymethylbenzyl, etc.) orcycloaliphatic alcohols (e.g., cyclohexanoyl). Alternatively, non-cyclicalcohols such as fluorocarbon alcohols, aliphatic alcohols, aminogroups, vinyl ethers, and epoxides may be used.

Preferably, the silicon-containing polymer (before attachment of thechromophore) of a liquid deposited ARC ispoly(4-hydroxybenzylsilsesquioxane). Examples of other silsesquioxanepolymers include: poly(p-hydroxyphenylethylsilsesquioxane),poly(p-hydroxyphenylethylsilsesquioxane-co-p-hydroxy-alpha-methylbenzylsilsesquioxane),poly(p-hydroxyphenylethylsilsesquioxane-co-methoxybenzylsilsesquioxane),poly(p-hydroxyphenylethylsilsesquioxane-co-t-butylsilsesquioxane),poly(p-hydroxyphenylethylsilsesquioxane-co-cyclohexylsilsesquioxane),poly(p-hydroxyphenylethylsilsesquioxane-co-phenylsilsesquioxane),poly(p-hydroxyphenylethylsilsesquioxane-co-bicycloheptylsilsesquioxane),poly(p-hydroxy-alpha-methylbenzylsilsesquioxane),poly(p-hydroxy-alpha-methylbenzylsilsesquioxane-co-p-hydroxybenzylsilsesquioxane),poly(p-hydroxy-alpha-methylbenzylsilsesquioxane-co-methoxybenzylsilsesquioxane),poly(p-hydroxy-alpha-methylbenzylsilsesquioxane-co-t-butylsilsesquioxane),poly(p-hydroxy-alpha-methylbenzylsilsesquioxane-co-cyclohexylsilsesquioxane),poly(p-hydroxy-alpha-methylbenzylsilsesquioxane-co-phenylsilsesquioxane),poly(p-hydroxy-alpha-methylbenzylsilsesquioxane-co-bicycloheptylsilsesquioxane),poly(p-hydroxybenzylsilsesquioxane-co-p-hydroxyphenylethylsilsesquioxane),andpoly(p-hydroxy-alpha-methylbenzylsilsesquioxane-co-alpha-methylbenzylsilsesquioxane).

The Si containing polymers that can be used in a liquid deposited ARCpreferably have a weight average molecular weight, before reaction withthe cross-linking component, of at least 1000, more preferably a weightaverage molecular weight of 1000-10000.

The cross-linking component of the liquid deposited ARC is preferably acrosslinker that can be reacted with an SiO containing polymer in amanner which is catalyzed by generated acid and/or by heating. Thiscross-linking component can be inorganic or organic in nature. It can bea small compound (as compared with a polymer or copolymer) or a polymer,a copolymer, or a blend including at least two of any combination ofpolymers and/or copolymers, wherein the polymers include one monomer andthe copolymers include at least two monomers. Generally, thecross-linking component used in the liquid deposited antireflectivecoating compositions may be any suitable cross-linking agent known inthe negative photoresist art which is otherwise compatible with theother selected components of the composition. The cross-linking agentspreferably act to crosslink the polymer component in the presence of agenerated acid. Preferred cross-linking agents are glycoluril compoundssuch as tetramethoxymethyl glycoluril, methylpropyltetramethoxymethylglycoluril, and methylphenyltetramethoxymethyl glycoluril, availableunder the POWDERLINK trademark from American Cyanamid Company. Otherpossible cross-linking agents include: 2,6-bis(hydroxymethyl)-p-cresol,compounds having the following structures:

including their analogs and derivatives, such as those found in JapaneseLaid-Open Patent Application (Kokai) No. 1-293339, as well as etherifiedamino resins, for example methylated or butylated melamine resins(N-methoxymethyl- or N-butoxymethyl-melamine respectively) ormethylated/butylated glycolurils, for example as can be found inCanadian Patent No. 1 204 547. Other cross-linking agents such asbis-epoxies or bis-phenols (e.g., bisphenol-A) may also be used.Combinations of cross-linking agents may be used. The cross-linkingcomponent may be chemically bonded to the Si containing polymerbackbone.

In another embodiment, the cross-linking component is asilicon-containing polymer having at least one unit selected from asiloxane, silane, carbosilane, oxycarbosilane, silsesquioxane,alkyltrialkoxysilane, and tetra-alkoxysilane. The polymer is preferablya polymer, a copolymer, a blend including at least two of anycombination of polymers and/or copolymers, wherein the polymers includeone monomer and the copolymers include at least two monomers and whereinthe monomers of the polymers and the monomers of the copolymers areselected from a siloxane, silane, carbosilane, oxycarbosilane,silsesquioxane, alkyltrialkoxysilane, tetra-alkoxysilane, unsaturatedalkyl substituted silsesquioxane, unsaturated alkyl substitutedsiloxane, unsaturated alkyl substituted silane, an unsaturated alkylsubstituted carbosilane, unsaturated alkyl substituted oxycarbosilane,carbosilane substituted silsesquioxane, carbosilane substitutedsiloxane, carbosilane substituted silane, carbosilane substitutedcarbosilane, carbosilane substituted oxycarbosilane, oxycarbosilanesubstituted silsesquioxane, oxycarbosilane substituted siloxane,oxycarbosilane substituted silane, oxycarbosilane substitutedcarbosilane, and oxycarbosilane substituted oxycarbosilane.

The acid generator used in the liquid deposited ARC composition ispreferably an acid generator compound that liberates acid upon thermaltreatment. A variety of known thermal acid generators are suitablyemployed such as, for example, 2,4,4,6-tetrabromocyclohexadienone,benzoin tosylate, 2-nitrobenzyl tosylate and other alkyl esters oforganic sulfonic acids, blocked alkyl phosphoric acids, blockedperfluoroalkyl sulfonic acids, alkyl phosphoric acid/amine complexes,perfluoroalkyl acid quats wherein the blocking can be by covalent bonds,amine and quaternary ammonium. Compounds that generate a sulfonic acidupon activation are generally suitable. Other suitable thermallyactivated acid generators are described in U.S. Pat. Nos. 5,886,102 and5,939,236; the disclosures of these two patents are incorporated hereinby reference. If desired, a radiation-sensitive acid generator may beemployed as an alternative to a thermally activated acid generator or incombination with a thermally activated acid generator. Examples ofsuitable radiation-sensitive acid generators are described in U.S. Pat.Nos. 5,886,102 and 5,939,236. Other radiation-sensitive acid generatorsknown in the resist art may also be used as long as they are compatiblewith the other components of the antireflective composition. Where aradiation-sensitive acid generator is used, the cure (cross-linking)temperature of the composition may be reduced by application ofappropriate radiation to induce acid generation which in turn catalyzesthe cross-linking reaction. Even if a radiation-sensitive acid generatoris used, it is preferred to thermally treat the composition toaccelerate the cross-linking process (e.g., for wafers in a productionline).

The antireflective coating compositions used in the liquid depositionprocess preferably contain (on a solids basis) in a suitable solventcommonly known to those skilled in the art (i) from 10 wt % to 98 wt. %of a polymer including M, more preferably from 70 wt. % to 80 wt. %,(ii) from 1 wt % to 80 wt. % of cross-linking component, more preferablyfrom 3 wt. % to 25%, most preferably from 5 wt. % to 25 wt. %, and (iii)from 1 wt. % to 20 wt. % acid generator, more preferably 1 wt. % to 15wt. %.

After liquid depositing the ARC, a post deposition baking step istypically, but not necessarily always, used to remove unwantedcomponents, such as solvent, and to effect crosslinking. When performed,the baking step is conducted at a temperature from 60° C. to 400° C.,with a baking temperature from 80° C. to 300° C. being even morepreferred. The duration of the baking step varies and is not critical tothe practice of the present invention. The baked and previously liquiddeposited ARC may further undergo a post curing treatment process. Thispost curing treatment may include one of the post treatments used abovefor the optional dielectric cap. As such, the various post treatmentsand conditions used above in treating the optional dielectric cap areincorporated herein by reference.

In addition, the composition of the starting precursor used in liquiddeposition as well as the introduction of oxygen, nitrogen, fluorinecontaining precursors also allows the tunability of these films. Ineither embodiment mentioned above, the ARC's optical constants aredefined here as the index of refraction n and the extinction coefficientk. In general, the ARC can be modeled so as to find optimum opticalparameters (n and k values) of ARC as well as optimum thickness. Thepreferred optical constants of the ARC are in the range from n=1.4 ton=2.6 and k=0.01 to k=0.78 at a wavelength of 248, 193 and 157, 126 nmand extreme ultraviolet (13.4 nm) radiation.

In addition to the above, the ARC in any embodiment has good etchselectivity during pattern transfer. Etch selectivities of 1.5-4 to 1 ofthe ARC to the cured dielectric materials can be obtained. Furthermore,the use of the ARC of described above (vapor or liquid deposited)maintains the pattern and structural integrity after curing of thepatterned dielectric materials. This is critical as the ARC is retainedas a permanent part of the final interconnect stack.

In some embodiments of the invention, the dielectric cap and the ARC ofmaterial stack 16 can be combined into a graded cap that includesproperties of both a dielectric cap layer and an ARC. Such a graded capincludes at least a lower region that includes elements of a dielectriccap and an upper region that includes elements of an ARC. The graded capcan be formed utilizing any of the methods mentioned above in formingthe dielectric cap and/or ARC.

After forming the material stack 16 on an upper surface of substrate 12,a first low k material 18 is formed on an uppermost surface of thematerial stack 16, and then a second low k material 20 is formed on anupper exposed surface of the first low k material 18. The first low kmaterial 18 and the second low k material 20 are comprised of differentdielectric materials each having a dielectric constant of less than 4.0,typically less than 3.8. The different dielectric materials havedifferent etch rates associated therewith as is understood by thoseskilled in the art. Illustrative examples of low k materials that can beemployed as the first low k material 18 and the second low k material 20include, but are not limited to, silsesquioxanes, C doped oxides (i.e.,organosilicates) that include atoms of Si, C, O and H, thermosettingpolyarylene ethers, doped silicate glass materials, and cured PPLKmaterials as described above. In some embodiments, the cured PPLKmaterial can be derived from a positive-tone or negative-tone PPLKcomposition. The term “polyarylene” is used in this disclosure to denotearyl moieties or inertly substituted aryl moieties which are linkedtogether by bonds, fused rings, or inert linking groups such as, forexample, oxygen, sulfur, sulfone, sulfoxide, carbonyl and the like. Insome embodiments of the present disclosure, at least one of the firstand second low k materials (18, 20) is composed of one of the ARCmaterials mentioned above.

The thickness of the first and second low k materials (18, 20) may varydepending on the material employed for each of the layers as well as thetechnique that was used in forming the same. Typically, the first andsecond low k materials (18, 20) have a thickness from 5 nm to 2 μm, witha thickness from 50 nm to 500 nm being more typical. The first andsecond low k materials (18, 20) can be formed utilizing any conventionaldeposition process including, but not limited to, chemical vapordeposition, plasma enhanced chemical vapor deposition, evaporation,chemical solution deposition and spin-on coating. When one of the firstand second low k materials (18, 20) is composed of a cured PPLKmaterial, a PPLK material is first formed as described herein andthereafter a curing step is performed any time after deposition of thePPLK material that converts the PPLK material into a cured and permanentlow k material.

After forming the first and second low k materials (18, 20), a firstpatterned photoresist 22 having at least one first opening 24 is formedatop the upper surface of the second low k material 20. The firstpatterned photoresist 22 is composed of any conventional photoresistmaterial including organic photoresist materials, inorganic photoresistmaterials, or hybrid photoresist materials. The first patternedphotoresist 22 can be composed of a PPLK material that has beensubjected to exposure, development and curing. In some embodiments, thefirst patterned photoresist 22 is formed by lithography which includesapplying a photoresist material to the upper surface of the second low kmaterial 20, exposing the photoresist material to a desired pattern ofradiation, and developing the exposed resist utilizing a conventionalresist developer. In one embodiment, a maskless exposure step isemployed to pattern the photoresist material. In another embodiment, theexposure step includes the use of a mask having the desired patterntherein. The at least one first opening 24 that is present in the firstpatterned photoresist 22 exposes an upper surface portion of the secondlow k material 20.

Referring now to FIG. 2, there is illustrated the initial structure 10shown in FIG. 1 after transferring the at least one first opening 24into the second low k material 20 forming a patterned second low kmaterial 20′ having the at least one first opening 24′ and subsequentremoval of the first patterned photoresist 22. The transferring of theat least one first opening 24 into the second low k material 20 can beperformed utilizing an etching process including dry etching or chemicalwet etching. When dry etching is employed, one of reactive ion etching,ion beam etching, plasma etching, or laser ablation can be employed.When a chemical wet etching process is employed, a suitable chemicaletchant that selectively removes the exposed portion of the second low kmaterial 20 can be employed. After patterning the second low k material20, the patterned photoresist 22 can be removed utilizing a conventionalresist stripping process such as ashing.

Referring now to FIG. 3, there is illustrated the structure of FIG. 2after forming a second patterned photoresist 26 including at least onesecond opening 28 therein atop the patterned second low k material 20′as well as within the at least one first opening 24′ in the patternedsecond low k material 20′. The second patterned photoresist 26 caninclude one of the photoresist materials mentioned above for the firstpatterned photoresist 22. Also, the second patterned photoresist 26having the at least one second opening 28 can be formed using thelithographic process mentioned above for forming the first patternedphotoresist 22.

Referring now to FIG. 4, there is illustrated the structure of FIG. 3after transferring the at least one second opening 28 into the patternedsecond low k material 20′ and the underlying first low k material 18 andremoval of the second patterned photoresist 26. The transferring of theat least one second opening 28 into the first and second low k materialscan be performed utilizing one of the etching processes mentioned aboveand the removal of the second patterned photoresist 26 can be achievedby utilizing a conventional resist stripping process, as also mentionedabove. In FIG. 4, reference numeral 20″ denotes the patterned second lowk material that includes at least one first opening 24′ and an upperportion of the now transferred at least one second opening, andreference numeral 18′ denotes the patterned first low k material thatincludes a lower portion of the now transferred at least one secondopening. The upper and lower portions of the at least one second openingare collectively labeled as 28′ and are hereinafter just referred to asthe at least one second opening 28′. The at least one second opening 28′that is within both the first and second low k materials exposes anupper surface portion of the underlying material stack 16. Although notshown in the drawings, the exposed portion of material stack 16 throughthe at least one second opening 28′ can be opened utilizing any standardetching process that is capable of selectively removing the exposedportions of material stack 16.

Referring now to FIG. 5, there is illustrated the structure of FIG. 4after forming a patterned and cured photo-patternable low k (PPLK)material 30 having a plurality of electrically conductive filled regions32 therein. The patterned and cured photo-patternable low k (PPLK)material 30 also includes gaps 36. The gaps 36 are located betweenneighboring electrically conductive filled regions. As shown in FIG. 5,at least one of the plurality of electrically conductive filled regionsis located within the at least one second opening 28′ and one of thegaps 36 is located above and connected with the at least one firstopening 24′ located within the patterned second low k material 20″.

The patterned and cured PPLK material 30 is a positive-tone PPLKmaterial initially formed utilizing a deposition process including, forexample, spin-on-coating, dip coating, brush coating, blade coating,chemical solution deposition, and ink-jet dispensing. After applying thePPLK material, a post deposition baking step is typically, but notnecessarily always, employed to remove unwanted components, such assolvent. When performed, the baking step can be conducted at atemperature from 40° C. to 200° C., with a baking temperature from 60°C. to 140° C. being more preferred. The duration of the baking stepvaries from 10 seconds to 600 seconds and is not critical herein. Thethickness of the applied PPLK material may vary depending on therequirement of the chip and the technique used to form the same as wellas the material make-up of the applied PPLK material. Typically, theapplied PPLK material has a thickness from 1 nm to 50000 nm, with athickness from 20 nm to 5000 nm being more typical.

After applying the PPLK material, the applied PPLK material is processedto include at least one, typically, a plurality, of electricallyconductive filled regions 32. The electrically conductive filled regions32 are typically separated from the PPLK material by a diffusion barrier34. The electrically conductive filled regions 32 are formed within theapplied PPLK material by conventional lithography (including a patternwise exposure step). An optional post-exposure baking may be required toeffect the photochemical reactions. When performed, the baking step isconducted at a temperature from 60° to 200° C., with a bakingtemperature from 80° to 140° C. being more preferred. The duration ofthe baking step varies and is not critical to the practice of thepresent invention. After exposure and post-exposure baking, the latentimages are developed with an appropriate developer, usually an aqueousbase solution, such as 0.26N tetramethylammoniahydroxide (TMAH)solution, to form a relief PPLK pattern.

The pattern wise exposing process can be accomplished in a variety ofways, including, for example, through a mask with a lithography stepperor a scanner with an exposure light source of G-line, I-line (365 nm),Deep UV (248 nm, 193 nm, 157 nm, 126 nm), Extreme UV (13.4 nm), or anelectron beam. The exposing process may be performed in a dry mode or animmersion mode. The pattern-wise exposing process also includes directwriting without the use of a mask with, for example, light, electronbeam, ion beam, and scanning probe lithography. Other patterningtechniques that can be used include contact printing techniques such asnanoimprint lithography, embroising, micro contact printing, replicamolding, microtransfer molding, micromolding in capillaries andsolvent-assisted micromolding, thermal assisted embroising, injectprinting, and the like.

After the pattern wise exposure and development, the thus formed openingwithin the applied PPLK material is filled with an electricallyconductive material and planarized. In some embodiments, a diffusionbarrier 34, which may comprise Ta, TaN, Ti, TiN, Ru, RuTaN, RuTa, W, WNor any other material that can serve as a barrier to preventelectrically conductive material from diffusing through, is typicallyformed prior to filling the opening within the PPLK material with theelectrically conductive material. The diffusion barrier 34 can be formedby a deposition process such as, for example, atomic layer deposition(ALD), chemical vapor deposition (CVD), plasma enhanced chemical vapordeposition (PECVD), physical vapor deposition (PVD), sputtering,chemical solution deposition, or plating. In some embodiments (notshown), the diffusion barrier 34 may comprise a combination of layers.The thickness of the diffusion barrier 34 may vary depending on theexact means of the deposition process employed as well as the materialand number of layers employed. Typically, the diffusion barrier 34 has athickness from 4 to 40 nm, with a thickness from 7 to 20 nm being moretypical.

Following the formation of the diffusion barrier 34, the remainingregion of each opening formed into the developed PPLK material is filledwith an electrically conductive material forming electrically conductivefilled regions 32. The electrically conductive material includes, forexample, polySi, an electrically conductive metal, an alloy comprisingat least one electrically conductive metal, an electrically conductivemetal silicide, an electrically conductive nanotube or nanowire,graphene or combinations thereof. In one embodiment, the electricallyconductive material is a conductive metal such as Cu, W, Al, Mn, Co, Ta,Ti or a combination thereof, with Cu or a Cu alloy (such as AlCu) beinghighly preferred in some embodiments of the present invention. Theelectrically conductive material is filled into the opening of thedeveloped PPLK material utilizing a conventional deposition processincluding, but not limited to CVD, PECVD, sputtering, chemical solutiondeposition or plating. In some embodiments, electrochemical plating ispreferred technique used in filling the opening within the developedPPLK material with the electrically conductive material.

After forming the plurality of electrically conductive filled regions 32and optionally the diffusion barrier 34 within openings formed into thePPLK material, the PPLK material including the plurality of electricallyconductive filled regions 32, is subjected to a second exposure step anddevelopment step that forms gaps 36 in the PPLK material betweenneighboring electrically conductive filled regions. The second exposurestep used in forming gaps 36 includes the same lithographic exposurestep mentioned above in forming the openings in the as-deposited PPLKmaterial in which the electrically conductive filled regions 32 weresubsequently formed. The development step used in forming gaps 36 isalso the same as described above in forming the electrically conductivefilled regions 32. After forming gaps 36 into the PPLK material, acuring step is performed which converts the PPLK material into apatterned and cured PPLK material 30. It is observed that the patternedand cured PPLK material 30 remains as a permanent on-chip low-kinterconnect dielectric material within the structure.

Curing is performed by a thermal cure, an electron beam cure, anultra-violet (UV) cure, an ion beam cure, a plasma cure, a microwavecure or a combination thereof. The conditions for each of the curingprocesses are well known to those skilled in the art and any conditioncan be chosen as long as it converts the previously processed PPLKmaterial into a patterned and cured PPLK material 30 that maintainsstructure fidelity and provides good electrical and mechanicalproperties. The cured product of processed PPLK material has adielectric constant of 4.3 or less, with a dielectric constant of lessthan 3.8 being more typical.

In one embodiment, the irradiation cure step is performed by acombination of a thermal cure and an ultra-violet (UV) cure wherein thewavelength of the ultra-violet (UV) light is from 50 nm to 300 nm andthe light source for the ultra-violet (UV) cure is a UV lamp, an excimer(exciplex) laser or a combination thereof. The excimer laser may begenerated from at least one of the excimers selected from the groupconsisting of Ar₂*, Kr₂*, F₂, Xe₂*, ArF, KrF, XeBr, XeCl, XeCl, XeF,CaF₂, KrCl, and Cl₂ wherein the wavelength of the excimer laser is inthe range from 50 nm to 300 nm. Additionally, the light of theultra-violet (UV) cure may be enhanced and/or diffused with a lens orother optical diffusing device known to those skilled in the art.

In another embodiment, the curing step is a combined UV/thermal cure.This combined UV/thermal cure is carried out in a UV/thermal cure moduleunder vacuum or inert atmosphere, such as N₂, He or Ar. Typically, theUV/thermal cure temperature is from 100° C. to 500° C., with a curetemperature from 300° C. to 450° C. being more typical. The duration ofthe UV/thermal cure is from 0.5 min to 30 min with a duration from 1 nmto 10 min being more typical. The UV cure module is designed to have avery low oxygen content to avoid degradation of the resultant dielectricmaterials.

Referring now to FIG. 6, there is illustrated the structure of FIG. 5after performing a lateral etching process that forms an expanded widthgap 38 within the patterned first low k material 18′. The expanded widthgap 38 is located beneath and connected to the first opening 24′ withinthe patterned second low k material 20″, which first opening 24′ is inturn located beneath and connect with one of the gaps 36 formed in thepatterned and cured PPLK material 30. As shown, the expanded width gap38 has a width that is greater than the overlying and connected firstopening 24′ and one of gaps 36. The lateral etching process that can beemployed in the present invention includes wet etching or a combinationof plasma modification and wet cleaning. For example, oxygen plasma, NH₃plasma, or N_(2/3) plasma can be used to isotropically modify theexposed portion of the first low k material. The modified portion of thefirst low k material is subsequently removed by a wet etch (e.g.,diluted HF dip), while the unmodified part of the low-k is not etchedaway.

Referring to FIG. 7, there is illustrated the structure of FIG. 6 afterforming a dielectric cap 40 atop the patterned and curedphoto-patternable low k material 30 forming air gaps 42 within thestructure. Dielectric cap 40 that is employed in the present disclosureincludes one of the dielectric capping materials mentioned above thatcan be used within material stack 16. The dielectric cap 40 can beformed as described above and its thickness is within the range ofthickness given for dielectric cap that can be employed within materialstack 16.

It is observed that the processing steps mentioned above in connectionwith FIGS. 1-7 provide an air gap-containing interconnect structure suchas shown, for example, in FIG. 7, that includes a substrate 12, amaterial stack 16 located on an upper surface of the substrate 12, apatterned first low k material 18′ located on an uppermost surface ofthe material stack 16, a patterned second low k material 20″ located onan upper surface of the patterned first low k material 18′, a patternedand cured photo-patternable low k (PPLK) material 30 located on an uppersurface of the patterned second low k material 20″, and a dielectric cap40 located on an upper surface of the patterned and cured PPLK material30, wherein said patterned and cured PPLK material 30 has a plurality ofelectrically conductive filled regions 32 and air gaps 42 locatedtherein in which at least a lower portion of one of the plurality ofelectrically conductive filled regions (see, the electrically conductivefilled region 32 on the far left hand side of FIG. 7) extends throughthe patterned first and second low k materials (18′ and 20″), and whereone of the air gaps (see the air gap 36 on the far right hand side ofFIG. 7) includes an extended width lower portion (see element 38) thatis present in the first patterned low k material 18′ and is connectedwith said one of the air gaps in the patterned and cured PPLK 30 by anopening (24′) within the patterned second low k material 20″.

Reference is now made to FIGS. 8-14 which illustrate a second embodimentof the present disclosure. The second embodiment begins by providing theinitial structure 100 shown in FIG. 8. Specifically, the initialstructure 100 shown in FIG. 8 includes from bottom to top, a substrate12, a material stack 16, a first low k material 18, a second low kmaterial 20 and a self-assembled co-polymer mask 102 including aplurality of openings 104 therein. The substrate 10, the material stack16, the first low k material 18 and the second low k material 20 are thesame as those described above in connection with the initial structure10 shown in FIG. 1. As such, the above description for substrate 10, thematerial stack 16, the first low k material 18 and the second low kmaterial 20 is applicable here for this embodiment and is thusincorporated herein by reference.

As stated above, the initial structure 100 also includes aself-assembled co-polymer mask 102 including a plurality of openings 104therein which is located atop the second low k material 20.

The self-assembled co-polymer mask 102 having the plurality of openings104 is made from a self-assembling block copolymer system that iscapable of self-organizing into nanometer-scale patterns. Theself-assembling block copolymer system typically contains two or moredifferent polymeric block components that are immiscible with oneanother. Under suitable conditions, the two or more immiscible polymericblock components separate into two or more different phases on ananometer scale and thereby form ordered patterns of isolated nano-sizedstructural units. Such ordered patterns of isolated nano-sizedstructural units formed by the self-assembling block copolymers can beused for fabricating nano-scale structural units in semiconductordevices. Specifically, dimensions of the structural units so formed aretypically in the range of 10 to 40 nm, which are sub-lithographic (i.e.,below the resolutions of the lithographic tools). Further, theself-assembling block copolymers are compatible with conventionalsemiconductor processes.

In this embodiment of the invention, a thin layer of a self-assemblingblock copolymer (having a thickness typically ranging from 20 nm to 100nm) is first applied over the second low k material 20 and then annealedto form an ordered pattern containing repeating structural units. Manydifferent types of block copolymers can be used for practicing thisembodiment of the instant disclosure. As long as a block copolymercontains two or more different polymeric block components that areimmiscible with one another, such two or more different polymeric blockcomponents are capable of separating into two or more different phaseson a nanometer scale and thereby form patterns of isolated nano-sizedstructural units under suitable conditions. In one embodiment, the blockcopolymer consists essentially of first and second polymeric blockcomponents A and B that are immiscible with each other. The blockcopolymer may contain any numbers of the polymeric block components Aand B arranged in any manner. The block copolymer can have either alinear or a branched structure. In one embodiment, the block copolymeris a linear diblock copolymer having the formula of A-B.

Specific examples of suitable block copolymers that can be used mayinclude, but are not limited to,polystyrene-block-polymethylmethacrylate (PS-b-PMMA),polystyrene-block-polyisoprene (PS-b-PI),polystyrene-block-polybutadiene (PS-b-PBD),polystyrene-block-polyvinylpyridine (PS-b-PVP),polystyrene-block-polyethyleneoxide (PS-b-PEO),polystyrene-block-polyethylene (PS-b-PE),polystyrene-b-polyorganosilicate (PS-b-POS),polystyrene-block-polyferrocenyldimethylsilane (PS-b-PFS),polyethyleneoxide-block-polyisoprene (PEO-b-PI),polyethyleneoxide-block-polybutadiene (PEO-b-PBD),polyethyleneoxide-block-polymethylmethacrylate (PEO-b-PMMA),polyethyleneoxide-block-polyethylethylene (PEO-b-PEE),polybutadiene-block-polyvinylpyridine (PBD-b-PVP), andpolyisoprene-block-polymethylmethacrylate (PI-b-PMMA).

The specific structural units formed by the block copolymer aredetermined by the molecular weight ratio between the first and secondpolymeric block components A and B. For example, when the ratio of themolecular weight of the first polymeric block component A over themolecular weight of the second polymeric block component B is greaterthan about 80:20, the block copolymer will form an ordered array ofspheres composed of the second polymeric block component B in a matrixcomposed of the first polymeric block component A. When the ratio of themolecular weight of the first polymeric block component A over themolecular weight of the second polymeric block component B is less than80:20 but greater than 60:40, the block copolymer will form an orderedarray of cylinders composed of the second polymeric block component B ina matrix composed of the first polymeric block component A. When theratio of the molecular weight of the first polymeric block component Aover the molecular weight of the second polymeric block component B isless than 60:40 but is greater than 40:60, the block copolymer will formalternating lamellae composed of the first and second polymeric blockcomponents A and B. Therefore, the molecular weight ratio between thefirst and second polymeric block components A and B can be readilyadjusted in the block copolymer of the present invention, in order toform desired structural units.

In one embodiment, the ratio of the molecular weight of the firstpolymeric block component A over the molecular weight of the secondpolymeric block component B ranges from 60:40 to 40:60, so that theblock copolymer of the present invention will form alternating layers ofthe first polymeric block component A and the second polymeric blockcomponent B.

In this embodiment, one of the components A and B can be selectivelyremovable relative to the other, thereby resulting in orderly arrangedstructural units composed of an un-removed component, i.e., theself-assembled co-polymer mask 102. For example, when the secondpolymeric block component B is selectively removable relative to thefirst polymeric block component A, orderly arranged trenches can beformed. In one embodiment, the block copolymer used for forming theself-assembled periodic patterns is PS-b-PMMA with a PS:PMMA molecularweight ratio ranging from 60:40 to 40:60.

Typically, mutual repulsion between different polymeric block componentsin a block copolymer is characterized by the term χN, where χ is theFlory-Huggins interaction parameter and N is the degree ofpolymerization. The higher χN, the higher the repulsion between thedifferent blocks in the block copolymer, and the more likely the phaseseparation therebetween. When χN>10 (which is hereinafter referred to asthe strong segregation limit), there is a strong tendency for the phaseseparation to occur between different blocks in the block copolymer.

For a PS-b-PMMA diblock copolymer, χ can be calculated as approximately0.028+3.9/T, where T is the absolute temperature. Therefore, χ isapproximately 0.0362 at 473K (≈200° C.). When the molecular weight(M_(n)) of the PS-b-PMMA diblock copolymer is approximately 64 Kg/mol,with a molecular weight ratio (PS:PMMA) of approximately 66:34, thedegree of polymerization N is about 622.9, so χN is approximately 22.5at 200° C.

In this manner, by adjusting one or more parameters such as thecomposition, the total molecular weight, and the annealing temperature,the mutual compulsion between the different polymeric block componentsin the block copolymer can be readily controlled to effectuate desiredphase separation between the different block components. The phaseseparation in turn leads to formation of self-assembled periodicpatterns containing ordered arrays of repeating structural units (i.e.,spheres, cylinders, or lamellae.

In order to form the self-assembled periodic patterns, the blockcopolymer is first dissolved in a suitable solvent system to form ablock copolymer solution, which is then applied onto a surface of thesecond low k material 20 to form a thin block copolymer layer, followedby annealing of the thin block copolymer layer, thereby effectuatingphase separation between different polymeric block components containedin the block copolymer.

The solvent system used for dissolving the block copolymer and formingthe block copolymer solution may comprise any suitable solvent,including, but not limited to, toluene, propylene glycol monomethylether acetate (PGMEA), propylene glycol monomethyl ether (PGME), andacetone. The block copolymer solution preferably contains the blockcopolymer at a concentration ranging from 0.1% to 2% by total weight ofthe solution. More preferably, the block copolymer solution contains theblock copolymer at a concentration ranging from 0.5 wt % to 1.5 wt %. Inone embodiment, the block copolymer solution comprises 0.5 wt % to 1.5wt % PS-b-PMMA dissolved in toluene or PGMEA.

The block copolymer solution can be applied by any suitable technique,including, but not limited to, spin casting, coating, spraying, inkcoating, dip coating, etc. Preferably, the block copolymer solution isspin cast onto the surface of the second low k material 20 to form athin block copolymer layer thereon.

After application of the thin block copolymer layer onto the surface ofthe second low k material 20, the entire structure is annealed toeffectuate micro-phase segregation of the different block componentscontained by the block copolymer, thereby forming the periodic patternswith repeating structural units. Annealing of the block copolymer can beachieved by various methods known in the art, including, but not limitedto, thermal annealing (either in a vacuum or in an inert atmospherecontaining nitrogen or argon), ultra-violet annealing, laser annealing,solvent vapor-assisted annealing (either at or above room temperature),and supercritical fluid-assisted annealing, which are not described indetail here in order to avoid obscuring the invention.

In one embodiment, a thermal annealing step is carried out to anneal theblock copolymer layer at an elevated annealing temperature that is abovethe glass transition temperature (T_(g)) of the block copolymer, butbelow the decomposition or degradation temperature (T_(d)) of the blockcopolymer. More preferably, the thermal annealing step is carried out anannealing temperature between 200° C.-300° C. The thermal annealing maylast from less than 1 hour to 100 hours, and more typically from 1 hourto 15 hours. In an alternative embodiment of the present invention, theblock copolymer layer is annealed by ultra-violet (UV) treatment.

After annealing, one of the polymeric components of the self-assembledblock copolymer can be selectively removable relative to the other,thereby resulting the formation of the self-assembled co-polymer mask102. The removal of one of the components is achieve utilizing anysuitable solvent that selectively removes one of the polymericcomponents of the self-assembled block copolymer relative to the othercomponent. The remaining component of the self-assembled block copolymeris used as mask 102 in the present disclosure. As such, mask 102 hasregularly repeating structure units having a sub-lithographic width asmentioned above. The openings 104 within the mask 102 also have asub-lithographic width since they are formed by selectively removing oneof the phase separated polymeric components from the annealed blockcopolymer.

Referring to FIG. 9, there is shown the structure of FIG. 8 afteretching the exposed portions of the second low k material 20 utilizingthe self-assembled co-polymer mask 102 as an etch mask and subsequentremoval of mask 102. In FIG. 9, reference numeral 20′ denotes thepatterned second low k material that now includes sub-lithographicopenings 106 located therein. The etching of the exposed portions of thesecond dielectric low k material 20 is performed utilizing one of dryetching and chemical wet etching. When dry etching is employed, one ofreactive ion etching, plasma etching, ion beam etching or laser ablationcan be employed. When a chemical etch process is employed, a suitablechemical etchant can be used. After etching, the mask 102 is removedutilizing a conventional stripping process such as, for example, plasmaetching, reactive ion etching or wet chemical etching.

Referring to FIG. 10, there is shown the structure of FIG. 9 afterforming a patterned photoresist 108 having at least one opening 110therein that exposes at least one of the sub-lithographic openings 106within the previously patterned second low k material 20′. The patternedphotoresist 108 includes one of resist materials mentioned above for thefirst patterned photoresist 22 and the patterned photoresist 108 isprocessed using one of the lithographic techniques mentioned above aswell.

Referring now to FIG. 11, there is illustrated the structure of FIG. 10after etching exposed portions of the first low k material 18 utilizingthe patterned photoresist 108 as an etch mask and removal of thepatterned photoresist 108. The etching of the exposed portions of thefirst low k material 18 forms a patterned first low k material 18′having at least one sub-lithographic sub-lithographic opening 110located therein which extends to an upper surface of material stack 16.The etching of the exposed portions of the second low k material 18includes one of dry etching and wet chemical etching. The patternedphotoresist 108 is removed utilizing a conventional resist strippingprocess such as, for example, ashing. Although not shown in thedrawings, the exposed portions of the material stack 16 throughsub-lithographic opening 110 can be opened utilizing any conventionaletching technique well known to those skilled in the art.

Referring to FIG. 12, there is depicted the structure of FIG. 11 afterforming a patterned and cured photo-patternable low k material 30 havinga plurality of electrically conductive filled regions 32 and gaps 36located therein, wherein at least one of the plurality of electricallyconductive filled regions 32 is located within sub-lithographic opening110. An optional diffusion barrier 34 can be located between each of theregions 32 and the PPLK material 30. This step of this embodiment of thepresent disclosure includes the materials and processing steps mentionedabove in forming the structure shown in FIG. 5 of the first embodiment.As such, the various like materials and processing steps mentioned abovein forming the patterned and cured PPLK material 30 having gaps 36 and aplurality of electrically conductive filled regions 32 are alsoapplicable here and are thus incorporated herein by reference.

Referring to FIG. 13, there is depicted the structure of FIG. 12 afterperforming a lateral etch that forms an expanded width gap 38 in thepatterned first low k material 18′. The expanded width gap 38 is formedutilizing the lateral etching process mentioned above in the firstembodiment of the invention. As shown, the expanded width gap 38connects at least two of the gaps 36 that are present in the overlyingpatterned and cured PPLK material 30.

Referring to FIG. 14, there is depicted the structure of FIG. 13 afterforming a dielectric cap 40 atop the PPLK material 30 forming air gaps42 within the structure. The dielectric cap 40 is the same as thatdescribed above in the first embodiment of the present invention. Assuch, the various materials and processing techniques mentioned above informing dielectric cap 40 in the first embodiment are incorporatedherein for this embodiment of the instant disclosure.

It is observed that the processing steps mentioned above in connectionwith FIGS. 8-14 provide an air gap-containing interconnect structuresuch as shown, for example, in FIG. 14, that includes a substrate 12, amaterial stack 16 located on an upper surface of the substrate 12, apatterned first low k material 18′ located on an uppermost surface ofthe material stack 16, a patterned second low k material 20′ located onan upper surface of the patterned first low k material 18′, a patternedand cured photo-patternable low k (PPLK) material 30 located on an uppersurface of the patterned second low k material 20′, and a dielectric cap40 located on an upper surface of the patterned and cured PPLK material30, wherein said patterned and cured PPLK material 30 has a plurality ofelectrically conductive filled regions 32 and air gaps 42 locatedtherein in which at least a lower portion of one of the plurality ofelectrically conductive filled regions (see, the electrically conductivefilled region 32 on the far left hand side of FIG. 14) extends throughthe patterned first and second low k materials (18′ and 20′), and whereone of the air gaps (see the air gap 36 on the far right hand side ofFIG. 14) includes an extended width lower portion (see element 38) thatis present in the first patterned low k material 18′ and is connectedwith said one of the air gaps in the patterned and cured PPLK 30 by anopening (24′) within the patterned second low k material 20′.

While the present invention has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present invention. It is therefore intended that the presentinvention not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

1. An air gap-containing interconnect structure comprising: a substrate;a material stack located on an upper surface of the substrate; apatterned first low k material located on an uppermost surface of thematerial stack; a patterned second low k material located on an uppersurface of the patterned first low k material; a patterned and curedphoto-patternable low k material located on an upper surface of thepatterned second low k material; and a dielectric cap located on anupper surface of the patterned and cured photo-patternable low kmaterial, wherein said patterned and cured photo-patternable low kmaterial has a plurality of electrically conductive filled regions andair gaps located therein in which at least a lower portion of one of theplurality of electrically conductive filled regions extends through thepatterned first and second low k materials, and where one of the airgaps includes an extended width lower portion that is present in thefirst patterned low k material and is connected with said one of the airgaps in the patterned and cured photo-patternable low k material by anopening within the patterned second low k material.
 2. The airgap-containing interconnect structure of claim 1 wherein the pluralityof electrically conductive filled regions as well as the air gaps withinthe patterned and cured photo-patternable low k material have asub-lithographic width.
 3. The air gap-containing interconnect structureof claim 1 wherein said patterned and cured photo-patternable low kmaterial is derived from a positive-tone photo-patternable low-kmaterial.
 4. The air gap-containing interconnect structure of claim 1wherein said material stack includes a dielectric cap, an antireflectivecoating or both a dielectric cap and an antireflective coating.
 5. Theair gap-containing interconnect structure of claim 1 wherein saidmaterial stack is a patterned material stack, and said lower portion ofone of the plurality of electrically conductive filled regions extendsthrough said patterned material stack.
 6. The air gap-containinginterconnect structure of claim 1 wherein said plurality ofelectronically conductive filled regions includes Al, Cu, W, Mn, Co, Ta,Ti or a combination thereof.
 7. The air gap-containing interconnectstructure of claim 1 wherein said first patterned low k material andsaid second patterned low k material are composed of different low kmaterials having different etch rates.
 8. The air gap-containinginterconnect structure of claim 7 wherein at least one of the substrate,the first patterned low k material and the second patterned low kmaterial is comprised of an antireflective coating.
 9. The airgap-containing interconnect structure of claim 1 wherein some of the airgaps stop on the upper surface of the second patterned low k material.10. The air gap-containing interconnect structure of claim 1 wherein theextended width lower portion is located beneath at least two of theplurality of electrically conductive filled regions within the patternedand cured photo-patternable low k material material.
 11. A method offorming an air gap-containing interconnect structure comprising:providing a patterned mask on a surface of an initial structure, saidinitial structure including a substrate, a material stack located on anupper surface of the substrate, a first low k material located on anuppermost surface of the material stack, and a second low k materiallocated on an upper surface of said first low k material, wherein saidpatterned mask has at least one first opening that exposes a portion ofsaid second low k material; etching the exposed portion of the patternedsecond low k material utilizing the patterned mask as an etch mask toform a patterned second low k material having said one first openingtherein; forming a patterned photoresist on an upper surface of saidpatterned second low k material, wherein a portion of said patternedphotoresist fills said at least one first opening within the patternedsecond low k material, said patterned photoresist having at least onsecond opening that exposes a portion of said patterned second low kmaterial; etching the exposed portion of the second low k material aswell as underlying portions of the first low k material utilizing thepatterned photoresist as an etch mask to form a patterned second low kmaterial having said one first opening and an upper portion of said atleast one second opening therein and a patterned first low k materialhaving a lower portion of said at least one second opening therein;forming a patterned and cured photo-patternable low k material having aplurality of electrically conductive filled regions and gaps locatedtherein atop the patterned second low k material, wherein at least oneof the plurality of electrically conductive filled regions is locatedwithin the at least one second opening and wherein one of the gaps islocated above and connected with the at least one first opening locatedwithin the patterned second low k material; performing a lateral etchingprocess that forms an expanded width gap within the patterned first lowk material which is located beneath and connected with the at least onefirst opening formed in the patterned second low k dielectric material;and forming a dielectric cap atop the patterned and curedphoto-patternable low k material forming air gaps at least within thephoto-patternable low k material.
 12. The method of claim 11 wherein thepatterned mask is a patterned photoresist formed by lithography.
 13. Themethod of claim 11 wherein the patterned mask is self-assembledco-polymer mask formed utilizing a self-assembling block copolymer,annealing the self-assembling block copolymer into a self-assembledblock copolymer and removing at least one of polymeric components of theself-assembled block copolymer.
 14. The method of claim 13 wherein saidself-assembled co-polymer mask has sub-lithographic features.
 15. Themethod of claim 11 wherein said material stack includes a dielectriccap, an antireflective coating or both a dielectric cap and anantireflective coating.
 16. The method of claim 11 wherein said materialstack is a patterned material stack, and a lower portion of one of theplurality of electrically conductive filled regions extends through saidpatterned material stack.
 17. The method of claim 11 wherein saidpatterned and cured photo-patternable low k material includes applying apositive-tone photo-patternable low k composition, first exposing theapplied positive-tone photo-patternable low k composition to radiation,developing the exposed portions of the applied positive-tonephoto-patternable low k composition, filling the developed regions withat least an electrically conductive material, second exposing anddeveloping to form said gaps, and curing.
 18. The method of claim 17wherein said curing includes a thermal cure, an electron beam cure, anUV cure, an ion beam cure, a plasma cure, a microwave cure or anycombinations thereof.
 19. The method of claim 11 wherein said lateraletching process includes wet etching or a combination of plasmamodification and wet cleaning.
 20. The method of claim 11 wherein saidplasma modification includes using an oxygen plasma, a NH₃ plasma, or aN_(2/3) plasma which isotropically modifies an exposed portion of thepatterned first low k material, and wherein the modified portion issubsequently removed by a diluted HF dip.